1. Field of the Invention
The present invention relates to a color sorting apparatus for agricultural products capable of sorting products based on optically sensed characteristics using a light source with visible light spectra or a near-infrared ("near-IR") spectra.
2. Description of the Prior Art
Commonly owned U.S. Pat. No. 4,454,029, of which Applicant Codding is a named inventor, relates to a bichromatic sorter for agricultural products. These sorters have been primarily used to detect unacceptable agricultural products based on color of the product, such as coffee beans, peanuts and the like. There were certain types of relatively smaller, usually granular, agricultural products, such as rice grains, which required only monochromatic or gray level to sort to reject unacceptable products. Although the '029 sorter is capable of sorting products using two color illumination levels, the sorter employs only a visible spectrum illumination source. Some products cannot be sorted using normally visible light buy may be differentiated using light in the near-IR range. For instance, tree nuts, such as almonds, require a lower frequency light to distinguish between acceptable and unacceptable products. Lower frequency light is also useful in distinguishing between agricultural products and foreign materials, such as stems, glass and plastics, which are often inadvertently included with the products during harvest or subsequent processing.
Commonly owned U.S. Pat. No. 4,697,709, of which Applicant Codding is a named inventor, describes a monochromatic sorting apparatus having a plurality of optical stations. Each station is composed of a plurality of optical sensors which are capable of sensing light reflected from a stream of product. The stream is illuminated by fluorescent lamps. The apparatus is capable of using only one source of illumination (e.g. fluorescent) and is therefore not capable of sorting products which require differentiation based on their near-IR spectra.
U.S. Pat. No. 4,466,544 relates to a sorting apparatus having a plurality of movable filters which can be remotely actuated such that a specific filter may be selected for use depending on the nature of the product being sorted. This eliminates the need to physically remove and replace filters each time the product being sorted is changed, thereby making the apparatus more economical and efficient. However, the apparatus is designed to operate with only one type of light source, thereby limiting its capabilities to sorting only those products which can be differentiated using a light source of only a single spectra (e.g. visible light).
U.S. Pat. No. 5,779,058 involves a color sorting apparatus for grains. This type of sorter has an illumination device for illuminating the grain, and an optical detector with an optical detection section for receiving the light from the illuminated grain. The illumination device employs a source having spectral energy distribution in both the visible light region and the near infrared region. The optical detection section of the optical detection device includes a first light receiving sensor having a high sensitivity to the visible light region and a second light receiving sensor having a high sensitivity to the near infrared region. While this apparatus is intended to be capable of sorting products using both the visible spectra and the near-IR spectra, it was more complex and expensive than a machine having a single type of sensor and illumination source. In addition, the '058 apparatus uses a halogen light source to generate the near-IR illumination. Halogen light has typically required a greater number of bulbs to provide requisite illumination, as well as consumed significantly more power. The power consumed generated a great deal of undesirable heat, as compared to, for instance, an incandescent or fluorescent bulb.